A patient with pseudocholinesterase deficiency receives succinylcholine during induction of anaesthesia. Which of the following best explains the prolonged paralysis observed?

## Pseudocholinesterase Deficiency and Succinylcholine Metabolism **Key Point:** Succinylcholine is metabolised by plasma pseudocholinesterase (butyrylcholinesterase). Deficiency of this enzyme results in markedly prolonged paralysis because the drug cannot be rapidly hydrolysed. ### Normal Metabolism of Succinylcholine 1. Succinylcholine is a quaternary ammonium compound (water-soluble) 2. Rapidly hydrolysed by plasma pseudocholinesterase in the blood 3. Normal duration: 5–10 minutes 4. Metabolites are renally excreted ### Pseudocholinesterase Deficiency **High-Yield:** Pseudocholinesterase deficiency (also called butyrylcholinesterase deficiency or atypical plasma cholinesterase) is an autosomal recessive condition that leads to: - **Prolonged apnoea** (inability to breathe spontaneously) lasting hours instead of minutes - Accumulation of unchanged succinylcholine in plasma - Continued neuromuscular blockade until the drug is slowly eliminated unchanged via the kidneys ### Types of Pseudocholinesterase Deficiency | Type | Enzyme Activity | Duration of Paralysis | Frequency | | --- | --- | --- | --- | | **Normal (EE)** | 100% | 5–10 minutes | ~70% | | **Heterozygous (EA)** | ~50% | 15–20 minutes | ~25% | | **Homozygous (AA)** | <10% | 2–8 hours | ~1 in 3,500 | **Mnemonic:** **SABER** — Succinylcholine Apnoea Butyrylcholinesterase Enzyme Reduced **Clinical Pearl:** Patients with pseudocholinesterase deficiency require: - Prolonged mechanical ventilation and sedation - Monitoring of neuromuscular blockade - Reassurance that paralysis is temporary - Genetic counselling and family screening - Medical alert identification **Warning:** Do NOT give repeated doses of succinylcholine to a patient with pseudocholinesterase deficiency — the drug will accumulate and paralysis will be even more prolonged.